1. Field of the Invention
The present invention relates to a vertical impact crusher for crushing pieces of ore or adjusting the grain size of ore and, more particularly, to a vertical impact crusher having a rotor provided with improved, durable hard chips at its discharge gates.
2. Description of the Related Art
An exemplary vertical impact crusher pertinent to the present invention will be described with reference to FIGS. 5 to 8. As shown in FIG. 5, a vertical impact crusher 1 comprises a vertical drive shaft supported for rotation by a bearing unit 38, a rotor 2 mounted on the vertical drive shaft, a feed device 10 disposed in its upper central portion, and a hopper 11 disposed over the feed device 10. As shown in FIGS. 6, 7 and 8, the rotor 2 is a generally cylindrical box comprising a top rotor disk 7, a bottom rotor disk 8, three side walls arranged between the top rotor disk 7 and the bottom rotor disk 8 at intervals so as to form discharge gates therebetween, top liners 3 attached to the inner surface of the top rotor disk 7, bottom liners 4 attached to the inner surface of the bottom rotor disk 8, a central distributor 9 fixedly provided on the bottom rotor disk 8, three blades 12 arranged at equal angular intervals on the inner surface of the side walls 13 so as to extend radially inward, and three gate blocks 14 each disposed contiguously with one vertical edge of the side wall 13. Dead stock 15 of the material is formed in spaces each formed by the blade 12, the gate block 14 and the side wall 13 during the rotation of the rotor 2. As shown in FIGS. 8 and 9, abrasion resistant hard chips 5a and 5b are attached detachably and one over the other to the extremities of the gate blocks 14, respectively. Cemented carbide chips 21a and 21b of a hardness higher than that of the hard chips 5a and 5b are embedded in the edges of the hard chips 5a and 5b, respectively.
When the rotor 2 is rotated at a high rotating speed on the vertical drive shaft, the material fed through the feed device into the rotor 2 is caused to flow along the dead stock 15 and the hard chips 5a and 5b and is discharged through the gates 16 by centrifugal force as shown in FIG. 6. Then, the material collides against anvils 17 or a dead ring, not shown, and is crushed into grains of desired grain sizes.
During the rotation of the rotor 2 of the conventional vertical impact crusher 1 at a high rotating speed, the material flowing along the dead stock 15 tends to flow further toward the middle portion of the vertical stack of the hard chips 5a and 5b as indicated by an arrow in FIG. 11(b). Consequently, the new hard chips 5a and 5b, and the new cemented carbide chips 21a and 21b having shapes as shown in FIGS. 10(a) and 11(a) are abraded with time in shapes as shown in FIGS. 10(b) and 11(b); that is, the lower portions d.sub.1 of the upper hard chip 5a and the upper cemented carbide chip 21a, and the upper portions d.sub.2 of the lower hard chip 5b and the lower cemented carbide chip 21b are abraded. Then, to use further the thus abraded hard chips 5a and 5b, and the thus abraded cemented carbide chips 21a and 21b, the hard chips 5a and 5b provided respectively with the cemented carbide chips 21a and 21b are replaced on each gate block 14 with each other to stack the hard chips 5a and 5b on each gate block 14 as shown in FIGS. 10(c) and 11(c), in which the stack of the abraded hard chips 5a and 5b has a central portion in which the flow of the material is concentrated thicker than in upper and lower portions. The replacement of the hard chips 5a and 5b with each other enables the further use of the abraded hard chips 5a and 5b and the abraded cemented carbide chips 21a and 21b.
However, since the section of the surface of the stack of the abraded hard chips 5a and 5b provided with the abraded cemented carbide chips 21a and 21b is a smooth curve falling uniformly from the middle portion toward the upper and lower ends as shown in FIG. 10(c) and the shape of a portion of the dead stock 15 near the cemented carbide chips 21a and 21b conforms to the shapes of the surfaces of the hard chips 5a and 5b, the material tends to flow along the most abraded portions of the cemented carbide chips 21a and 21b as indicated by arrows in FIG. 11(c) to further abrade the abraded portions of the cemented carbide chips 21a and 21b. Thus, the effect of the replacement of the hard chips 5a and 5b with each other for the extension of the life of the hard chips 5a and 5b, and the cemented carbide chips 21a and 21b is not as significant as expected.